Motor vehicles are generally equipped with a hydraulic service brake system in which pressure is built up in a master brake cylinder, and is transmitted to wheel brakes via brake lines filled with a hydraulic medium, in accordance with a brake pedal actuation by the driver. It is often also possible for an autonomous pressure build-up to be performed according to demand, and independently of a brake pedal actuation, by an electronic control unit. Driving safety functions such as driving dynamics regulation (Electronic Stability Control, ESC), and increasingly also assistance functions such as a holding function of the vehicle (Active Vehicle Hold, AVH), are provided by means of a driver-independent brake actuation of said type. Said holding function can, by means of an autonomous pressure build-up and a shutting-in of brake pressure in the wheel brakes, automatically hold the vehicle at a standstill on a gradient even over a relatively long period of time. If the vehicle is equipped with an electrically actuable parking brake system, a transfer from the service brake system to the parking brake system takes place under certain conditions (for example if the driver opens the door).
DE 103 45 485 A1, which is incorporated by reference, discloses a brake device having a service brake and parking brake function, which brake device comprises a hydraulic pressure-generating unit for the hydraulic application of the brake device, a self-locking, preferably electric force generating unit for additional application of the brake device, and a brake-application element which is acted on both by the hydraulic pressure generating device and also the additional force generating device. In the case of an actuation of the parking brake function, the additional brake application takes effect after the hydraulic brake application. The level of the brake-application force of the additional brake application is higher than the level of the brake-application force of the hydraulic brake application. An electric parking brake which acts jointly with a hydraulic service brake on a brake-application device provided with friction lining is known under the name “integrated parking brake” (IPB).
EP 1 678 018 B1, which is incorporated by reference, discloses a method for stabilizing a motor vehicle which is braked at a standstill, which motor vehicle is equipped with a brake system which can be actuated independently of the driver and which comprises a service brake and a parking brake. After the vehicle comes to a standstill, a parking brake force which is to be generated by the parking brake for maintaining the vehicle standstill state is determined, and a service braking force which simulates the parking brake is generated independently of the driver by means of the service brake, whereupon the predetermined parking braking force is built up by means of the parking brake and, when or after the parking braking force is attained in the parking brake, the service brake is deactivated. This method is intended to prevent the vehicle from rolling away, which may occur in the case of a partially icy roadway as a result of the parking brake being provided for example only on the rear wheels, whereas the service brake acts on all of the wheels of the vehicle.
It is often the case that vehicles are equipped only with a hydraulic service brake at least one wheel, in particular at the front wheels, and with an integrated parking brake at least one wheel, in particular at the rear wheels. When a transfer from the hydraulic holding function of the service brake to the electric parking brake takes place in a vehicle equipped in this way, a retroaction of the parking brake on the hydraulic brake can lead to an undesired slow release of the brake pads and to slippage of the brake disk, with a disturbing noise being generated.